Locking nut and a fastening structure made up of the locking nut and a member being tightened

Abstract

The invention is intended to provide a fastening structure made up of a nut and a to-be-tightened member which does not get loose even when used in places where it is subject to large vibrations. The nut has a cylindrical female screw extension portion which projects from the seat of the nut and which has a female screw formed in the inner circumferential surface thereof. The to-be-tightened member which is on the male screw side is formed with a fastening hole into which the female screw extension portion is to be fitted. The inner surface of the fastening hole and the outer surface of the female screw extension portion are tapered so that there is a taper angle difference. As the nut is fastened onto the male screw, the female screw extension portion is pushed inwardly and deformed due to the taper angle difference so that the female screw formed on the female screw extension portion is pressed against the male screw. When, with the nut fastened in this way, the fastening force applied to the nut is removed, the female screw remains deformed and pressed against the male screw, preventing the nut from becoming loose.

What is claimed is: 
     
       1. A fastening structure, comprising: a nut and a to-be-tightened member;   a cylindrical female screw extension portion which projects from a seat of the nut and which has a female screw thread formed in the inner circumferential surface thereof;   a fastening hole formed in the to-be-tightened member into which the female screw extension portion is to be fitted;   whereby the inner surface of the fastening hole and the outer surface of the female screw extension portion are tapered such that there is a taper angle difference between the two surfaces and such that when the nut is fastened onto the male screw, the female screw extension portion is deformed inwardly due to the taper angle difference and pressed against the male screw, preventing the loosening of the nut; and   wherein between the nut and the to-be-tightened member is installed a dish spring which is deformed by fastening the nut and a spacer which is loosely fitted into the hole of the dish spring and is thicker than the thickness of the dish spring.   
     
     
       2. A fastening structure as claimed in claim 1, wherein the spacer is formed integral with the nut. 
     
     
       3. A fastening structure as claimed in claim 1, wherein the female screw extension portion is formed with at least one radially extending dividing groove. 
     
     
       4. A fastening structure comprising: a nut and a to-be-tightened member;   a cylindrical female screw extension portion which projects from a seat of the nut and which has a female screw thread formed in the inner circumferential surface thereof;   a washer having a fastening hole formed therein and adjacent to the to-be-tightened member, the female screw extension portion to be fitted into the fastening hole;   whereby the inner surface of the washer and the outer surface of the female screw extension portion are tapered such that there is a taper angle difference between the two surfaces and such that when the nut is fastened onto the male screw, the female screw extension portion is deformed inwardly due to the taper angle difference and pressed against the male screw, preventing the loosening of the nut; and   wherein between the nut and the to-be-tightened member is installed a dish spring which is deformed by fastening the nut and a spacer which is loosely fitted into the hole of the dish spring and is thicker than the thickness of the dish spring.   
     
     
       5. A fastening structure as claimed in claim 4, wherein the dish spring is installed between the washer and the to-be-tightened member, and the spacer is formed integral with the washer.